Processes for making dust-free, free-flowing, pigment products are exemplified by U.S. Pat. Nos. 4,127,421 to Ferrill, Jr. and 4,285,994 to Pearce et al. In an aqueous process, granules are formed by agitating an aqueous slurry of pigment often including a waxy material or polymeric material melting below 100.degree. C., and surfactant. By the aqueous process of Ferrill, Jr., essentially spherical granules having a diameter between about 0.5 and 1 mm, and containing more than 70 wt. % lead chromate, may be formed. The process provides a hydrocarbon-type resin in molten form, requires a cationic surfactant, and may use an anionic surfactant which may be sodium stearate.
By the process of Pearce et al, powdered pigment may be tumbled with a wax composition having an average particle size typically ranging between 300 and 500 microns, and with a suitable oil or liquid surfactant, to produce a product containing more than 70 wt. % pigment. Hot and cold granulation of cadmium pigment are described.
Also known as illustrated by U.S. Pat. No. 4,173,492 to Pollard, is a process for preparing coated pigment particles by mixing pigment and a suitable molten coating agent, cooling the resulting mixture to produce a solid mass, and breaking the solid mass into flakes. By the process of Pollard, presscake pigment is mixed with molten hydroxystearate wax having a melting point in the range of 52.degree. C. to 88.degree. C., under high shear conditions, to eventually provide flakes having a pigment loading in excess of 75%.
Despite the foregoing, commercially available, color concentrate is usually supplied in the form of pellets measuring approximately one-eighth inch by one-eighth inch. Typically, these pellets are formed by crossblending selected pigments, preblending the resulting pigment blend with a base resin, and hot melt compounding in specialized equipment such as a single screw or twin screw extruder, to pelletize. For coloring, the pellets are dispersed in a selected natural resin at a let down ratio usually ranging from one part of concentrate to from five to fifty parts of natural resin. However, it is known to be a difficult task to obtain good color uniformity when using color concentrate pellets, at a let down ratio of 50:1.
There continues to be a need to let down color concentrates at a ratio in excess of 50:1, for instance at a ratio of 60 or 70:1. Accordingly, an improved color concentrate is needed. The color concentrate should be dustless and advantageously will have good pourability. Improved dilution and dispersion characteristics of the color concentrate, when blended with natural resin, are necessary to provide color uniformity.